1. Field Of The Invention
The present invention relates to the art of papermaking and the machines that form paper as a continuous web.
2. Background Of The Invention
As practiced by the present state-of-the-art, papermachines produce a continuous, fourdrinier laid web at velocities of 1,000 to 3,000 feet per minute. In the course of processing and finishing, numerous opportunities are presented within the machine to break and therefore interrupt the web continuity. Along most of the machine length, a web break may have no consequence on the web production upstream of the rupture. Although the paper product at the point of rupture is unfinished, the fiber material substance of the unfinished product is recoverable as "broke" which is reslurried into pulp and recycled through the machine. Accordingly, the machine is rarely stopped in the event of a web rupture. Production of broke is allowed to continue until the web is rethreaded through the machine remainder.
There are, however, some negative consequences of continued broke production while the machine is rethreaded. The first and most obvious is the massive quantity of broke material that could be dumped, uncontrollably, upon the machine operating floor. Fortunately, this negative consequence is easily avoided by strategically breaking the web at one of several locations along the machine length. At these strategic locations, an opening is provided in the operating floor through which the unfinished web is routed directly into broke handling equipment.
The negative consequence of web breaks within specific process equipment may be far more damaging or destructive. In the cases of calenders and coaters, nip running rolls may be wrapped by the leading edge of the broken web. Subsequent production continues to build upon the wrap. Destructive consequences to the equipment follow quickly thereafter.
For these reasons, web detection instruments have been developed to continuously monitor machine web continuity. When the web ruptures, one of these instruments downstream of the break will signal the failure. Upon signal, an appropriate web cutting or breaking mechanism upstream of the rupture point will act to break the web a second time but at one of the strategic locations.
Traditionally, the strategic break was made manually: by snapping the web edge with fingers or a hand along an accessible, and unsupported portion of the web route. Now, the break is made mechanically with a jet of air or water: but still at one edge of the web. Once the web edge is broken, web tensile stress continues the tear across the machine.
A full width cut of the web i.e. instantaneous severance of the web across the full width thereof, is most desirable. This, however, necessarily requires mechanical equipment. If perceived in the context of a knife or shear, automatic operation is hazardous to people working around the equipment. Probabilities are too great that some human body part will be in the shear or knife plane when operation occurs.
It is therefore, an object of the present invention to provide a mechanism which instantly severs a papermachine web across the entire width thereof without jeopardizing the safety of human attendants.
Another object of the present invention is to provide a papermachine web severing mechanism having no shearing elements or sharp edges.
Another object of the present invention is to provide a papermachine web severing mechanism that ruptures the entire web width along a line substantially perpendicular to the machine running direction.